The invention concerns monitoring the guiding of a magnetic tape of a cassette into a working position in recording and playback equipment and similarly the disengagement and unloading thereof from the equipment.
In videotape equipment of the oblique recording track type the magnetic tape is looped helically about a rotating scanning device. In order to simplify the handling of the tape, the tape is stored and held in a cassette wound up on two cores or spools. For pulling out the tape provided in a cassette and to loop the tape around the revolving scanning device (threading procedure) there is disclosed in German Patent Application No. 37 19 159 a mechanism which provides several stationary and movable rollers which pull the tape out of the cassette and dispose it in a certain path around the scanning device. An unthreading procedure operates in a manner opposite to the threading.
The threading and unthreading mechanism of such magnetic tape equipment is commonly located in a closed casing. The user of the equipment or maintenance personnel cannot recognize during threading or unthreading how far the cassette has already been pulled into the tape recording and playback equipment or into what position the tape is pulled out of the cassette.